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In this work, the effects of in-plane shear stress on the thermal conductivities of two important kinds of graphene configurations (rectangular graphene and annular graphene) are investigated using molecular dynamics simulations. The various strain angles are set as θ = 0°, 3°, 5°, 10°, and 15° for rectangular graphene and θ = 0°, 3°, 5°, and 8° for annular graphene. A spectral energy density approach is applied to carry out phononic analyses of the two configurations under in-plane shear stress for the first time. It is found that for rectangular graphene, the thermal conductivity shows a significant decreasing trend from 239.6 to 79.1 W m−1 K−1 with the θ increasing from 0° to 15°. Besides, the application of shear stress can significantly widen the energy bands of branches, which indicates shorter phonon lifetimes. Further phononic analysis shows that most of the phonon scattering caused by in-plane shear stress emanates from the in-plane mode, which is an updated conclusion in this field. On the other hand, the thermal conductivity of annular graphene also shows a decreasing evolution with the increasing strain angles, but phonon transport in rectangular graphene is more susceptible to shear stress than in annular graphene due to a stronger phonon-boundary scattering in the latter configuration. In this work, the monotonically decreasing trends of the thermal conductivities of both graphene configurations with the increasing strain angle are different from the V-shape trend reported in the literature. Based on phononic analyses, it can be concluded that an abnormal increase of the thermal conductivities at a low shear stress can be attributed to the application of the AIREBO potential model in the literature. [ABSTRACT FROM AUTHOR]

Brown carbon (BrC) represents an important target for the "win-win" strategy of mitigating climate change and improving air quality. However, estimating co-benefits of BrC control remains difficult for China, partially because current measurement results are insufficient to represent the highly variable emission sources and meteorological conditions across different regions. In this study, we investigated, for the first time, the diurnal variations of BrC during two distinct seasons in a megacity in northeast China. The winter campaign conducted in January 2021 was characterized by low temperatures rarely seen in other Chinese megacities (down to about -20 ∘ C). The mass absorption efficiencies of BrC at 365 nm (MAE 365) were found to be ∼ 10 % higher at night. The variations of MAE 365 could not be explained by the influence of residential biomass burning emissions or secondary aerosol formation but were strongly associated with the changes of a diagnostic ratio for the relative importance of coal combustion and vehicle emissions (RS/N). Given that most coal combustion activities were uninterruptible, the higher nighttime MAE 365 in winter were attributed primarily to increased emissions from heavy-duty diesel trucks. The spring campaign conducted in April 2021 was characterized by frequent occurrences of agricultural fires, as supported by the intensive fire hotspots detected around Harbin and the more-than-doubled ratios of levoglucosan to organic carbon (LG/OC) compared to the winter campaign. In spring, the MAE 365 depended little on RS/N but exhibited a strong positive correlation with LG/OC , suggesting open burning emissions as the dominant influencing factor for BrC's light absorption capacity. MAE 365 were ∼ 70 % higher at night for the spring campaign, pointing to the prevalence of nighttime agricultural fires, which were presumably in response to local bans on open burning. It is noteworthy that the agricultural-fire emissions resulted in a distinct peak at ∼ 365 nm for the light absorption spectra of BrC, and candidates for the compounds at play were inferred to be aromatic species with nitro-functional groups. The presence of the ∼ 365 nm peak complicated the determination of absorption Ångström exponents for the agricultural-fire-impacted samples. In addition, the ∼ 365 nm peak became much less significant during the day, likely due to photobleaching of the relevant chromophores. [ABSTRACT FROM AUTHOR]

Despite the growing interest in understanding haze formation in Chinese megacities, air pollution has been largely overlooked for the Harbin–Changchun (HC) metropolitan area, located in the severe cold climate region in northeast China. In this study, we unfolded significant variations of fine particulate matter (PM 2.5) in HC's central city (Harbin) during two sequential heating seasons of 2018–2019 and 2019–2020, and we explored major drivers for the observed variations. The two campaigns showed comparable organic carbon (OC) levels but quite different OC sources. The biomass burning (BB) to OC contribution decreased substantially for 2019–2020, which was attributed primarily to the transition of local policies on agricultural fires, i.e., from the "legitimate burning" policy released in 2018 to the "strict prohibition" policy in 2019. Meanwhile, the contribution of secondary OC (OC sec) increased significantly, associated with the much more frequent occurrences of high relative humidity (RH) conditions during the 2019–2020 measurement period. Similar to OC sec , the major secondary inorganic ions, i.e., sulfate, nitrate and ammonium (SNA), also exhibited RH-dependent increases. Given the considerable aerosol water contents predicted for the high-RH conditions, heterogeneous reactions were likely at play in secondary aerosol formation even in the frigid atmosphere in Harbin (e.g., with daily average temperatures down to below - 20 ∘ C). In brief, compared to 2018–2019, the 2019–2020 measurement period was characterized by a policy-driven decrease of biomass burning OC, a RH-related increase of OC sec and a RH-related increase of SNA, with the first two factors generally offsetting each other. In addition, we found that open burning activities were actually not eliminated by the strict prohibition policy released in 2019, based on a synthesis of air quality data and fire count results. Although not occurring during the 2019–2020 measurement period, agricultural fires broke out within a short period before crop planting in spring of 2020, and this resulted in off-the-charts air pollution for Harbin, with 1 h and 24 h PM 2.5 concentrations peaking at ∼ 2350 and 900 µ g/m 3 , respectively. This study indicates that sustainable use of crop residues remains a difficult challenge for the massive agricultural sector in northeast China. [ABSTRACT FROM AUTHOR]

The objective of the current study was to analyze expression levels of synapse differentiation inducing 1-like (SYNDIG1L) and unc-13 homolog C (UNC13C) genes in different tissues, while single-nucleotide polymorphisms (SNPs) of two genes were associated with multiple thoracic vertebrae traits in both Small-tailed Han sheep (STH) and Sunite sheep (SNT). The expression levels of SYNDIG1L and UNC13C were analyzed in the brain, cerebellum, heart, liver, spleen, lung, kidney, adrenal gland, uterine horn, longissimus muscle, and abdominal adipose tissues of two sheep breeds with different thoracic vertebral number (TVN) sheep (T13 groups and T14 groups) by real-time quantitative polymerase chain reaction (RT-qPCR). Meanwhile, the polymorphisms of UNC13C gene g.52919279C > T and SYNDIG1L gene g.82573325C > A in T14 and T13 were genotyped by the Sequenom MassARRAY® SNP assay, and association analysis was performed with the TVN. The results demonstrated that UNC13C gene was extensively expressed in 11 tissues. The expression of UNC13C gene in longissimus muscle of T14 groups of STH was significantly higher than that of T13 groups (P<0.05). SYNDIG1L gene was overexpressed in brain and cerebellum tissues, and the expression level of UNC13C gene in the brain and cerebellum of T13 groups in SNT was significantly higher than that of T14 groups (P<0.01). Association analysis showed that SNPs found in the UNC13C gene had no significant effects on TVN for both two genes. The polymorphism of SYNDIG1L g.82573325C > A was significantly correlated with the TVN in both STH (P<0.05) and SNT (P<0.01). Taken together, the SYNDIG1L gene was related to thoracic vertebral development, and this variation may be potentially used as a molecular marker to select the multiple thoracic vertebrae in sheep. [ABSTRACT FROM AUTHOR]

This work employed theoretical and experimental methods to study the drag reduction performance of flexible channels for low Reynolds number pulsating flow. A novel theoretical model was proposed to describe flow in a flexible rectangular channel. According to the model, the drag reduction of the flexible channel was speculated. Subsequently, experiments were carried out to verify the theoretical results and to illuminate the drag reduction performance of the flexible channel in detail under the impacts of pulsating frequency, nondimensional velocity amplitude, average Reynolds number, and the thickness of the flexible wall. The results indicated that the flexible channel exhibited superior drag reduction performance for pulsating flow as compared to that for steady flow. Meanwhile, the drag reduction rate increased with the increase of pulsating frequency, nondimensional velocity amplitude, and average Reynolds number, and smaller thickness of the flexible wall was in favor of drag reduction at the same flow parameters. Moreover, the current experimental data were utilized to establish a correlation predicting the drag reduction rate of the flexible channel for pulsating flow, which fits 76.4% of 195 data within ±25%. [ABSTRACT FROM AUTHOR]